Fenbendazole is a broad-spectrum benzimidazole anthelmintic used in several species of animals to treat a wide range of intestinal helminth parasites. In cats, it is effective against most intestinal worms and also treats flukes and lungworms. It has a long track record of safety in animal species and is well tolerated in humans at therapeutic doses for extended periods. In vitro, fenbendazole exhibits moderate microtubule depolymerizing activity and has antitumor effects in some cancer cell lines.
In an experiment using SCID mice, 1 mg/mouse of fenbendazole administered orally every 24 hours for 12 days induced significant shrinkage in the size of tumors compared to control groups. In the same study, Dogra et al.  showed that fenbendazole binds to b-tubulin, thereby binding it and preventing the formation of new microtubules. It also inhibited RAS-related signaling pathway expression in cancer cells with a KRAS mutation, resulting in an antitumor effect.
Similarly, a 2-h treatment of fenbendazole in cell culture reduced the number of viable EMT6 cells (Figure 1), but did not affect yield-corrected surviving fractions (YCSF) in aerobic cultures. Severe hypoxia, however, significantly decreased the surviving fractions of the fenbendazole-treated cultures, whereas it had no effect on those treated under normal conditions.
Further, in vivo fenbendazole toxicity studies in Cape Griffons and White-backed Vultures (Gyps coprotheres) demonstrated similar results, suggesting that other species of the Gyps genus may be susceptible to fenbendazole toxicity as well. In addition, extra-label fenbendazole efficacy against nematodes has been shown against Aelurostrongylus abstrusus, Ancylostoma tubaeforme, Baylisascaris procyonis, Crenosoma vulpis, Eucoleus spp., Filaroides spp., Pearsonema spp., and Strongyloides spp.; for cestodes, it is effective against Taenia spp.; and for trematodes, it is effective against Heterocerca spp. fenben lab fenbendazol